Currently used hydraulically activated work vehicles, such as backhoes, front end loaders, skid steers, hydraulic cranes, etc. use fluid control valves to direct the motion of various functions on these machines, such as swinging, booming, bucket dipping and bucket rotation. These control valves allow fine control of the various functions as the associated valve spool is moved to and from its neutral position.
The typical function of hydraulic equipment currently uses valve timing, which is either slightly metered in, neutral or slightly metered out. Typically, valve designers avoid the use of heavy metering in or heavy metering out functions as a result of energy considerations. More specifically, depending upon the amount of metering, energy can be wasted since high metering restrictions usually result in the operation of the hydraulic pump such that the associated driving engine has to generate additional power to force fluid through restrictions associated with heavy metering. However, there are certain functions on hydraulic equipment, such as a backhoe, which are usually operated at relatively high pressures (e.g., the swinging motion), or having an overrunning load (e.g., the hydraulics associated with a boom) which have a potential to generate pressure appropriate to generate a metering out conditions. Most control valves have a spool which has metering notches which meter the flow when there is partial movement of the spool. Maintaining the control valve spool in a neutral position to prevent unwanted movement of a backhoe function resulting from fluid flow and pressure build-up through the spool metering notches is an important and desirable characteristic.
Existing devices for control valve locks include mounting a solenoid directly to the valve body to allow the solenoid rod to engage a recess in the valve spool. Locking of control valve spools using solenoids, in the part, required extensive use of levers as shown in U.S. Pat. No. 4,011,959. An alternative means for locking a valve spool in a desired location is use of a pin engaging a recessed area in the valve spool as disclosed in U.S. Pat. No. 4,793,378. Such arrangements require redesign of existing valve bodies to accommodate such locking devices which is expensive and in some cases not possible because of alignment difficulties. Retro-fitting control valves on equipment already in the market cannot be easily or inexpensively accomplished if the solenoid must be mounted on the control body.
Thus, there is a need for an interlock mechanism that will maintain a control valve spool in a neutral position to prevent fluid flow pressure from operating any of the work vehicle functions without selective control by an operator of the work vehicle. There is also a need for an interlock mechanism that can lock the control valve spool in a neutral position without mounting the actuator directly on the valve body. There is a further need for the ability to retro fit existing control valves with a valve lock without a complete redesign or extensive modifications to the valve body.